* The test tries to verify that Invite Server Transactions correctly change
states as specified by the rfc3261. The Reference Implementation is used
to send requests and a Tested Implementation ServerTransaction's states are
queried and compared to those in the state machine described in
section 17.2.1 of rfc3261

Tries to steer a TI server transaction through the following scenario
Proceeding-->Completed-->Confirmed-->Terminated. Apart from state
transitions, we also test, retransmissions and proper hiding/passing
of messages to the TU.